1. Field
The present invention relates generally to RF oscillators and more particularly to voltage control oscillators designed to provide low phase noise.
2. Prior Art
There a number of U.S. patent references relating to variable frequency oscillator circuits which exhibiting low phase noise including U.S. Pat. Nos. 5,357,218, 5,185,583, 5,512,862, 5,268,657, 5,625,327, and 4,593,256. One of the principle methods of producing low phase noise in a variable frequency oscillator that is found in all of these references is the use of a resonator circuit with a high loaded Q. The principal way of obtaining a high loaded Q is to tap into the resonator rather than connect directly across it. This method transforms the impedance placed across the tap to a higher impedance across the entire resonator, thereby raising the loaded Q of the resonator. All of the reference patents use a tapped resonator in one form or another. Most connect into a direct tap on an inductor; however, in U.S. Pat No. 5,625,327 the tap is made by a capacitive divider across the resonator.